The present invention relates generally to the design, manufacture and use of blow molded bottles made of polyesters, such as polyethylene terephthalate, and similar containers including footed bottoms having improved dimensional stability suitable for the filling and storage of carbonated beverages.
Various attempts have been made to construct a one-piece, self-supporting plastic container made of polyesters, such as polyethylene terephthalate, which will be able to be filled with and retain carbonated beverages at the pressures typically involved. Such a one-piece container requires the design of a base structure which will support the bottle in an upright position and will not bulge outwardly at the bottom. A variety of designs have been attempted following one of two principal lines of thought. One line of designs involves a so-called champagne base having a complete annular peripheral seating ring. Examples of such bottles are found in U.S. Pat. Nos. 3,722,726; 3,881,621; 4,108,324; 4,247,012; and, 4,249,666. Another variety of designs is that which includes a plurality of feet protruding downward from a curved bottom. Examples of this variety are to be found in U.S. Pat. Nos. 3,598,270; 4,294,366; 4,368,825; 4,865,206; and, 4,867,323.
Bottles using each of these general designs have, in the past, shown significant drawbacks. In order to prevent involution of the bottom of bottles using a champagne style, it was generally found necessary to incorporate a significant amount of resin in the base of the bottle thereby ensuring its stability at room temperature. This incorporation of significant amounts of resin in the base of the bottle had the effect of not only increasing the cost of the bottle, but also making it increasingly subject to drop impact failure.
Reasonably stable footed bottles could be made employing less resin, but the uneven orientation of the polymer in the footed area of the bottom often contributed to uneven post filling expansion of either one or more feet or the central portion of the bottom creating what is generally referred to as a "rocker." Further, it was recognized that the stability of the bottle was directly related to the size of the footprint of the bottle. Whereas some of the earlier designs were in the form of a plurality of nearly point-like feet spaced apart by about half the diameter of the bottle, more recent designs have tended toward a wider spacing of the feet with each foot designed to contact an increased area of the underlying surface. Examples of such containers are to be found in U.S. Pat. Nos. 4,865,206; 4,978,015; and 5,024,340, as well as PCT publication WO 86/05462.
Throughout the development of various improvements on the two basic designs has been the constant goal to develop a container of stable configuration using as little resin as possible thereby reducing the cost of the container while maximizing the utility of natural resources. Accordingly, it is proposed to construct a container suitable for cold filling and storage of carbonated beverages which utilizes some of the design criteria previously employed in connection with such one piece containers having large standing ring diameters, but which will overcome the observed problems associated with such containers.
One problem with containers of this type is that they are subject to occasional bottom failure believed to be caused by stress cracking associated with the high inlet pressure of the liquid with which the container is filled. The dissipation of the energy on the container bottom leads to the occurence of stress fractures permitting the migration of foreign matter which, after a period of time, can contribute to or result in subsequent bottom failure. Accordingly, a container bottom feature is needed to prevent the aforementioned phenomena from occurring which is strong and flexible enough to withstand and absorb the kinetic energy of the entering liquid when the container is filled.